Horizons Unlimited - The "Bible" for Adventure Motorcycle Travellers worldwide. Anything you ever wanted to know about riding motorcycles around the world, or around your own country. If it's not there, just ask on the HUBB forum, and you'll get lots of answers.
Iron Butt Association - Advocating safe, responsible long distance riding, worldwide.
BMWMOA - BMW Motorcycle Owners of America website.
The Chain Gang - BMW F650 owners' information site
The Ulysses Club - A motorcycle club for older (over 40 year old) riders, slowly spreading out to the rest of the world from Australia.